Tanks are used for a variety of purposes, including, but not limited to, storage vessels, reaction vessels and the like. Tanks designed to store treated potable water before sending the water to the distribution system are known as clear wells. Such tanks may be rectangular or circular in shape and generally have sufficient volume to retain water for a desired period, such as 30 minutes, to permit disinfection or other treatment of the water. Since the flow patterns through many tanks are not ideal, the tanks are designed with surplus volume to assure that all of the flow is retained for the desired time period. The geometry of the tank is used to help calculate what factor must be applied to determine the actual volume required to achieve the desired results. In this regard, based on the tank geometry, the total volume of the tank may end up being a factor of 2 or 3 times the ideal volume.
Tanks may also take a variety of forms and shapes. Circular tanks are very attractive from a construction cost standpoint since they generally can be built for much less than rectangular tanks. However, circular tanks do not have a convenient flow pattern, such as would be the case for a plug flow configuration found in a pipe. Prior attempts have used concentric tanks nested within the outer tank to help create multiple channels with a flow pattern that was more in keeping with the plug flow concept. However, the cost of this approach was too high in comparison to the cost for rectangular tanks.
Further, other flow patterns have been attempted. For example, a multiple pass design tank 10, such as shown in FIG. 1, uses long, straight baffles 12 to achieve results similar to plug flow. In this regard, the baffles 12 are parallel to each other dividing the tank 10 into long strips of different lengths which cause the fluid to make multiple passes across the tank, as illustrated by arrows 14.
Another approach has been attempted to build a spiral or “snake” baffle, such as shown in FIG. 2. In this form, the tank 16 includes a spiral or snake shaped baffle 18, which is positioned in the tank 16 causing the fluid to flow in a generally spiral manner in the tank 16 as shown by arrows 20. The flow can go from the periphery to the center or vice versa. However, such baffled designs are relatively expensive to construct.
As shown in FIG. 3, a further design attempt at spiral flow is illustrated. A tank 22 includes an inlet 24 and an inlet baffle 26 at a sidewall 28 of the tank 22. An opening 30 is created between the inlet baffle 26 and sidewall 28, which takes all of the incoming flow and directs the flow along the wall 28 in a vertical plane, beginning a spiral pattern. However, as the fluid flows along the sidewall 28, it eventually returns to the baffle 26, which disrupts the fluid flow, as shown by arrows 32. Once past the baffle 26, the fluid will flow in a generally spiral manner, as shown by arrows 34 to an outlet 36.
The baffle 26 may include a hinge 38 at one edge to permit the other edge of the baffle 26 to swing away from the sidewall 28. An adjusting mechanism (not shown) can increase or decrease the opening 30 of the baffle 26 into the tank 22 to maintain a consistent exit velocity based on a varying flow rate to the tank 22.
However, several shortcomings exist with this design. The inlet 24, especially on larger tanks, usually results in the inlet baffle 26 being a significant structure. Further, the inlet baffle 26 undesirably disturbs the spiral flow pattern, as shown at arrows 32. This disruption may have a negative impact on the residency time of the fluid in the tank such that the tank volume is not used efficiently. Further, some tank construction methods require building the cover or roof of the tank at the same time the walls are built. This may present a further problem as the baffle 26 is generally installed after the sidewalls are built and usually require one or more cranes for installation.
A further shortcoming with the design is that the inlet baffle 26 must be connected to the sidewall 28. Some tanks are designed to have a sidewall that will flex or tilt inwardly and outwardly with a change in the liquid level in the tank. Thus, the baffle also must be designed to be flexible to allow this movement without placing additional stress on the tank wall.